In reply to Tall Clare: I use a Marmot Alone Alone bivi (the two hooped variety) for my winter mountaineering. At 800g its light and my 6'4" self fits in easily with room to spare for boots and other bits.

The hoops mean it is not very cramped and rather pleasant to stay in.

There is a pic of it in my photo gallery.

Only thing is, it can be hard to get the two hooped variety in the UK - usually there is no rear hoop. But I contacted Marmot directly and they sorted one out for me.

Mesh door is an absolute must to stop the biting nasties, and allow you to vent on a warm summers night. I never got a good nights sleep fully sealing up a bivvy in summer temperatures at valley levels.

A pole at the head end helps air flow and stops the fabric touching your face, which always kept me a wake at night.

I bivvied for years but final went for a light tent, more comfortable, space to change out of the rain, somewhere to sit up, cook and read ect.

If you are still interetsed in a bivvy I have a mountain range double hooped bivy for sale, olive green, goretex, about 1.2 Kg's, but there are some pin holes in the base; £50. Cheaper way to try the idea out than spending £250+ on a new one.................

Occasionally, usually high up on a still clear night bivvying is excellent.

I flipped mine upside down and then rigged a tarp off with a few tent pegs and some paracord. Gives the bike a bit of protection, makes it harder to steal, and the air breeze keeps you nice and warm. I survived some pretty hefty downpours but not the dreaded mozzies - so I'd double it with a mosquito net. I had considered buying a hennessy hammock (or similar) and then just using it as a tarp and mozzie net when there weren't any suitable trees. Could be a lighter option for 2 people than two bivi bags.

Is he really set on a bivvy bag? I reckon a tarp is better and you always have the bike to use to set it up on if you have no trees. Sleeping in the rain in a bivvy bag is miserable, under a well pitched tarp it can be ok.

But on bags - Alpkit do an XL one I believe that many seem to rate highly.